Billed two years after cancellation

I cancelled my contract with Rain, at least before July 2022, due to not receiving any service from them. The router never worked and I was forced to get an alternative internet solution. At some point, there was an agreement to write off any amount due to them if I returned my router, which was done. The matter was closed and my account reflected that nothing was due owing.

TWO YEARS LATER, I receive a bill for an arbitrary amount, not linked to the previous amount which was billed, despite not having a router, despite having cancelled the contract, despite not having been billed by this company for two years.